The peracetic acid-type sterilizer has heretofore been widely used for sterilizing or pasteurizing food containers and the like (patent document 1). The peracetic acid-type sterilizer contains peracetic acid, acetic acid and hydrogen peroxide in an equilibrium state. However, the hydrogen peroxide, if its concentration is too high, tends to remain in the container and, therefore, must be washed away after the sterilization to a sufficient degree with aseptic water. Therefore, there has also been proposed a pasteurizing method by using a sterilizing composition solution obtained by adding a catalase capable of decomposing hydrogen peroxide to the peracetic acid-type sterilizer (patent document 2).
In the sterilizing method that uses the peracetic acid-type sterilizing composition solution, it is a practice to recover the peracetic acid-type sterilizing composition solution used for the sterilization, adjust the concentration thereof, and circulate the sterilizing composition solution to the sterilizing equipment to use it again. The peracetic acid-type sterilizer, usually, exhibits good sterilizing efficiency at temperatures of not lower than 60° C. To conduct the sterilization, therefore, the peracetic acid-type sterilizing composition solution is used in a heated state. On the other hand, if the peracetic acid-type sterilizer or the peracetic acid-type sterilizing composition solution is placed in a heated state, decomposition of the peracetic acid is accelerated causing an increase in the amount of the hydrogen peroxide and, therefore, a decrease in the sterilizing power. In using the peracetic acid-type sterilizing composition solution in a circulating manner, therefore, it has been attempted to cool the peracetic acid-type sterilizing composition solution once heated for sterilization at a temperature of 60 to 70° C. down to 35° C. or lower through a circulation passage other than the sterilizing unit (patent documents 3 and 4).